Easiest described as style points. Used by the 'haxx0r' community sometimes.
Dictionary
You cannot have a single 'st33'. My dad seemed to think you should be able to. That means he has 0 St33z.
See WhyItIsCoolToReplaceVowelsWithLetters?.
One page links to St33z:
lib/main.php:944: Notice: PageInfo: Cannot find action page